It turns out one of the bolts was a stupid toggle bolt and I couldn't get it out of the wall no matter what tricks I tried. I couldn't even get it to unscrew enough to let the toggle fall into the wall. I ended up making the hole bigger to get the bolt out and now I have a 2" hole to be fixed and then re-textured.
Bright idea #2: Replace the dryer vent and outside hood and foam and/or caulk all the little gaps.
Home Depot and Lowe's sell the same kind of replacement vents with hoods already attached. One type has a flexible aluminum pipe and a plastic vent hood. The other type is rigid aluminum or galvanized steel with a solid metal vent hood and is much more sturdy.
However, BOTH of them have attached pipes that are not long enough to make it through the wall and leave enough to attach the dryer vent hose!
So my new dilemma is how do I cut galvanized steel pipe down to size? I read that it basically requires a special kind of pipe vise and cutting tool but I guess I'll try to use a hacksaw or maybe tin-snips. Lowe's told me they can't do it even though they have a sign that says 'we can cut galvinized and iron pipes for you'.
Nothing ever goes as planned and every project requires multiple trips to the hardware or home improvement store...